Summary: Exabyte mysteries

From: Rudolf Baumann (
Date: Thu Oct 25 1990 - 07:55:55 CDT

>From! Thu Oct 25 13:55:22 1990 remote from ethz

I was definitely not the first which had problems with the differences
between normal tape cassettes (QIC) and the Exabyte cassettes. My original
question was:

> The driver allows me only to append files on the absolute end of
> recorded media. It is obviously not allowed to skip to file in the
> middle of an already written tape and overwrite from there towards the
> end. Is there a way around this silly (my opinion) behavior?

In fact it is possible to overwrite files beginning from a specific file
mark. The procedure is quite complicated and definitely not intuitive.
Because an Exabyte can only write given one of three conditions: (as Robert
E. Toense pointed out):

        1) tape is at the beginning of the media,
        2) the last tape motion involved a write of data,
        3) the last command wrote an eof.

Consequently one has to write an eof mark to overwrite data on tape. In
order to have only one such mark between two files one must backspace over
the file mark of the last file one wants to preserve and rewrite the mark.
For me the following sequence works if I want to write past file 10:

        mt -f /dev/nrst0 asf 10
        mt -f /dev/nrst0 bsfm 1
        mt -f /dev/nrst0 weof

now the drive is ready to accept other write commands!
Most people suggested to use 'bsf 1' but this didn't work for me, it was
not possible to write the file mark after this command.

Many thanks to all the people which responded so quickly: (Robert E. Toense) (John Valdes) sent a summary from an earlier survey (Rich Schultz) (Dennis Morse)
Rudolf E. Baumann
Institut fuer Molekularbiologie & Biophysik ruba@biophys.uucp
ETH Hoenggerberg (HPM G6) MOLEKULA@CZHETH5A.bitnet
CH-8093 Zuerich/Switzerland Tel. ++41 1 377 33 97

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